It is well known in the art that substantial force is required to insert a printed circuit board into a conventional mating edge connector due to the wiping engagement between the electrical contact pads on the board and the contact regions of the pins or springs in the mating connector. As the number of contacts increases, the force required to effect insertion also increases and will eventually reach a point where the force required will be excessive for practical use. Also, repeated insertion and extraction of a board into and from a corresponding mating connector will cause repeated wipings to occur between the contact pads and the contact springs and may result in excessive wear to the contact pads and to the contact regions of the contact springs.
A common solution to this problem is the zero insertion force (ZIF) type connector. In these connectors, the contact pins located in the connector are movable between two positions. In the first position, the pins are retracted from the board insertion path thereby allowing the unobstructed and low force insertion of the printed circuit board into the connector. In the second position, the contact pins are moved by an actuator into engaging contact with the contact pads of the board.
When designing a zero insertion force connector, mechanical tolerances of the printed circuit board and of the mating connector must be considered. These mechanical tolerances stem from unavoidable manufacturing deviations from piece to piece and from lot to lot as well as variations in mechanical dimensions due to environmental operating conditions. A prudent design of a zero insertion force connector intended for large volume production will ensure that every printed circuit board can mate with every connector under a worst-case accumulation of mechanical tolerances. Further, previous connectors have oppositely aligned contact pins which, under a worst-case design, will cause the contact pins of a dimensionally nominal connector to touch the opposite facing pins when the pins are actuated in the absence of a printed circuit board in the connector. This invention avoids such problems.
In a modular or expandable system using a plurality of zero insertion force connectors, often several of the connectors are vacant, i.e., without printed circuit boards. Esthetics or other constraints often require these vacant connectors to be in the actuated or closed state. If the opposite facing contact pins of the vacant and closed connectors touch each other thereby producing electrical short circuits, damage to the remaining electrical circuitry may result or erroneous signals may be generated.
It is therefore desirable to provide a zero insertion force type electrical connector that will not cause opposite facing contact pins to contact and short circuit when the pins are actuated in the absence of a printed circuit board within the connector. This connector must also maintain a conservative worst-case design philosophy to ensure compatability between any board/connector combination.
It is also desirable to minimize the printed circuit board surface area devoted to electrical connections, thereby preserving valuable space for board mounted electrical components. At the same time, these electrical connections should be arranged so that a high probability of contact is maintained to ensure reliable operation.